THE EFFECT OF SUBSTRATE ORIENTATION ON THE PROPERTIES OF LOW-TEMPERATURE MOLECULAR-BEAM EPITAXIAL GAAS

GaAs and related materials, grown by molecular beam epitaxy at 200-300 degrees C under normal, group V-rich conditions sire highly nonstoich iometric, with excess group V concentrations of up to 10(21) cm(-3), a nd the material properties are defect controlled. Here we report on co mparative studies of low temperature growth of GaAs on (100) substrate s and on (111)A, (111)B, (311)A, and (311)B surfaces. We show that mat erial grown on both the (111) faces, under As-rich conditions, becomes polycrystalline almost immediately after commencement of growth. We a ttribute this to faceting of the surface creating regions of excessive As incorporation and either directly nucleating misorientated growth or producing areas of extreme localized strain resulting in the breakd own of crystallinity. Layers grown on (311)A and (311)B surfaces are o f good crystalline quality but are highly nonstoichiometric in both ca ses, contrary to the anticipation that the (311)A surface, having fewe r available forward Ga bonds than the (100) or (311)B surfaces might h ave a lower affinity for As incorporation. We also describe the reduct ion of excess As incorporation into layers grown on both (311) surface s in the presence of Si or Be doping concentrations of 1 x 10(19) cm(- 3) or greater as we previously reported for layers grown on (100) subs trates. This is evidenced by the reduced lattice parameter and lower a bsorption in the near-band-edge infrared region due to As antisite def ects, compared to undoped material. Also, little or no hopping conduct ion is seen in Be doped layers although they are totally compensated. A proportion of donors are active in the Si doped layers and the condu ction mechanism seems to be normal band conductivity. Electrical activ ation of the Si donors and Be accepters can be increased, however, onl y after high temperature annealing. (C) 1997 American Institute of Phy sics.